My day job is doing aero analysis and design for a defense company. A big thing when we design planes is that to reduce drag, you want to capture the absolute minumum amount of air possible in the inlet. For the purposes ot a car, the inlet would be the grill opening. It's pretty common knowledge now, but ducting the radiator and blocking everything else off has huge benefits.
In my experience, a lot of people who work around certain things think they know a lot about it just because they're near it. Welders thinking they know structural design, contractors thinking they know architecture, and apparently Bob thinking he knows aerodynamics.